1. Field of the Invention
The present invention relates to a triplexer, and more particularly to a triplexer for separating an input signal into signals of three different frequency bands, and a multilayered structure thereof.
2. Description of the Related Art
Recently, mobile telecommunications systems have comprised more complex functions to meet a variety of requirements of consumers. Also, mobile terminals have had simpler and smaller components installed therein so as to be convenient to carry. One such conventional mobile terminal is a dual-band terminal that can process signals of two frequency bands together. Such a dual-band mobile terminal typically comprises a multilayered diplexer for receiving signals of two different frequency bands simultaneously through one antenna and separating the received signals from each other.
In the dual-band mobile terminal, the multilayered diplexer is generally adapted to receive signals of two different frequency bands, for example, a code division multiplex access (CDMA) frequency band (about 824-894 MHz) and a personal communication service (PCS) frequency band (about 1850-1990 MHz) at one input terminal and branch the received signals respectively to two output terminals. The multilayered diplexer has a laminated structure of a plurality of dielectric layers having conductive patterns of high and low pass filters formed thereon. Through the laminated structure, the multilayered diplexer acts to separate an input signal received through one antenna into signals of respective frequency bands and provide the separated signals respectively to frequency processing circuits associated with the respective frequency bands and disposed at the subsequent stage.
Furthermore, a global positioning system (GPS) function has recently been additionally provided in mobile terminals, resulting in a need for a triple-band system to separately process signals of three frequency bands (for example, f1=824-894 MHz, f2=1560-1580 MHz and f3=1850-1990 MHz).
For implementation of the triple-band system, conventional mobile terminals have further comprised a separate antenna in addition to an existing antenna, or another high pass filter provided between the existing antenna and a diplexer.
A detailed description will hereinafter be given of two types of triple-band systems employed in conventional mobile terminals.
FIGS. 1a and 1b are block diagrams of triple-band systems of conventional mobile terminals. With reference to FIG. 1a, one conventional mobile terminal comprises an existing antenna 2 for receiving signals of the f1 and f3 bands, and a separate antenna 4 for receiving a signal of the additional f2 band. The f1 and f3 band signals received at the existing antenna 2 are separated from each other by a typical diplexer 6. The f2 band signal received at the separate antenna 4 is processed through a band pass filter 8 associated with the f2 band.
Alternatively, as shown in FIG. 1b, in the other conventional mobile terminal, the existing antenna 2 functions to receive the f2 band signal as well as the f1 and f3 band signals, without employing the separate antenna. Further, the f2 or f3 band signal is separately extracted from among the received signals.
However, the above-described triple-band systems of the conventional mobile terminals have a disadvantage in that separate components must be additionally installed in the mobile terminals, resulting in an increase in cost and difficulties in realizing smallness and lightness of the terminals.
Moreover, in the case where the f2 frequency band is present between the f1 frequency band and the f3 frequency band, particularly adjacent to any one, for example, f3 of them, a signal of the f3 frequency band must be accurately branched off from the adjacent frequency band. However, it is hard to implement a unitary circuitry capable of accurately branching the signal of the f3 frequency band off from the adjacent frequency band, and such a circuitry has also not been proposed up to the present.